In order to produce the compounds represented by the general formula [I], first a process is used which comprises synthesizing the pyrroles having the general formula [II]: ##STR3## and then, the compound having the general formula II is treated with a formulating step, as heretofore described in the prior art (U.S. Pat. No. 4,303,667).
In the general formula [II], X and n have the same significances defined above.
Further, as to the process for producing the said pyrroles having the general formula [II], the conventional process is set forth below in which taking into consideration the reactivity of the pyrrole, both .alpha.-positions of pyrrole are protected with easily separable protective groups and then its .beta.-position is treated with a chlorination step. This process is well known.
But, those conventional processes utilize numerous procedures and those operations involves difficult steps, so that those processes can not be said to be an industrially desirable method. ##STR4##